1. Field of the Invention
The present invention generally relates to a correcting method, and in particular to a method of correcting a shift of a working position of a working tool for use in a robot manipulation system.
2. Description of the Prior Art
In a conventional method of correcting a shift in positioning of a working tool in a robot manipulation system, there has been suggested a method of correcting a shift of bead in alignment in the disclosure of e.g. Japanese Paten Laid Open Unexamined Publication 1-257593.
In this robot mechanical arrangement, the following briefly describes an example of a conventional correcting method for correcting a shift of a position of a working tool for a robot manipulator system. In the conventional method, as shown in FIGS. 5 and 6, in order to adjust a working point of a working tool of a robot, a contact piece member provided on the working tool is brought into contact with a specified jig. Then, an error between the working point of the working tool and a reference working point determined in control programming of the robot is calculated for use as an offset amount according to data of the contact positions, thereby eliminating troublesome problems in calculating the offset amount.
In the method as shown in FIGS. 5 and 6, it is noted that, in the case where a subject work for a robot is a welding operation, a welding torch 58 is used as a working tool which is fitted to the robot main body. A welding wire 58b serving as a kind of contact piece is provided on the welding torch 58 and a tip portion 58a of the welding wire is brought into contact with a specified jig 59. The jig 59 has three conductive plates (59a, 59b, 59c) installed generally in a three-dimensional relationship to each other within the operating range of the robot, so that the tip 58a of the welding wire is moved in three dimensional directions P0-P1, P0-P2, and P0-P3 to be brought into contact with each of the three conductive plates 59a through 59c.
The position data at a timing of detecting the contact between the tip 58a of the welding wire 58b and each of the three conductive plates of the jig 59 is stored in a storage portion of a robot controller 60. The detection of the contact is electrically performed by applying a voltage between the welding torch 58 and the jig 59 by a voltage applying unit (not shown). Then, a difference between the position data of the preceding contact position and the position data of the present contact position is calculated by an arithmetic method to thereby compute an error between the position of the tip 58a of the welding wire and the reference point determined in control programming of the robot. The obtained error is stored as an offset amount, and the position of the welding torch 58 is shifted in a direction of absorbing the offset amount. Thus, the tip position of the welding wire is aligned with the reference point determined in control programming of the robot to thereby correct a shift of bead caused in a welding work and the like.
In this conventional method, there has been employed a step of detecting an electrical contact between the contact piece of the welding torch and the three jig plates in three dimensional directions different from each other. However, in the conventional methods, there has been a problematic case such that a working tool per se can not be directly used as a contact piece member, for example, in the case where a non-conductive or electrically insulating member is used as a working tool in the robot manipulation for such as laser sealing, bonding material and the like.
In such a problematic case, it is necessary to further provided an additional detecting unit for detecting an electrical contact such as e.g. a limit switch which detects an electrical contact when a working tool is moved to a predetermined position. Since the detection of the electrical contact with the three conductive plates must be carried out in the three different directions in the conventional method, therefore three contact detecting units are further required for detecting the contacts with the three conductive plates, respectively, which increases the cost of the robot system, undesirably making the construction thereof more complex.